1. Field of the Invention
This invention relates to a method of installing a conduit below a grade by boring through the earth, and more particularly, to a method that includes the steps of pulling a cable through the earth along the course to be traveled by the conduit and marking the ends of the cable.
2. Description of the Prior Art
In the laying of underground conduits, as for example pipelines, the conduit is normally laid in a trench. However, when the course of the conduit intersects a highway, railroad, or like obstruction that cannot be trenched, a pathway for the conduit must be bored through the earth under the obstruction. Such boring is typically carried out by a method that includes digging pits on either side of the obstruction, forming a small diameter pilot hole between the two pits, commonly referred to as a bore pit and a come out pit, along the course to be traveled by the conduit, reaming the pilot hole to form a radially enlarged hole having a diameter sufficient to accommodate the conduit, and running the conduit through the radially enlarged hole.
The most difficult step in boring is the formation of the pilot hole. The pilot hole must run straight and exit the come out pit within a relatively small target. It has been found to be advantageous when running multiple crossings, i.e., where multiple adjacent parallel conduits are to be run, to form a pilot hole for the next adjacent conduit, not by drilling, but by pulling a cable through the earth adjacent the conduit. The cable is pulled through the earth by means of a blade-like structure known as a wing extending radially outwardly from the conduit. The cable is attached to the wing, and as the conduit is pushed or pulled across the crossing, the wing slices through the earth and strings the cable therebehind. After the cable has been pulled across, the hole formed thereabout may be reamed to accommodate a conduit.
One problem that has plagued the boring industry is the installation of conduits adjacent previously installed conduits. Conduit easements are expensive, and it is in the easement owner's interest to maximize the number of conduits running through the easement. Accordingly, it is desirable to install conduits with a minimum of space therebetween. The desired spacing is on the order of one foot. However, it is presently virtually impossible to successfully install a new conduit closer than about three feet away from an existing conduit. This is because there exists for a radius of about three feet around an existing conduit a zone of soil that is disturbed and has an anomalous moisture content. If one attempts to drill a pilot hole within the disturbed radius, the pilot bit will drift toward the previously existing conduit. Accordingly, the pilot hole must presently be formed outside the disturbed radius.
It is, therefore, an object of the present invention to provide a method of installing a conduit adjacent a previously installed conduit without the necessity of drilling a pilot hole.